from enum import Enum
import sys
 
BIG_NUM = 2000000000
MOD = 1000000007
EPS = 0.000000001
 
class Point():
    def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
 
def calc_len(a,b):
    from math import sqrt
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))
 
x1,y1,x2,y2 = map(float,input().split())
 
p1 = Point(x1,y1)
p2 = Point(x2,y2)
 
print("%.10f"%calc_len(p1,p2)) from enum import Enum import sys sys BIG_NUM = 2000000000 BIG_NUM 2000000000 MOD = 1000000007 MOD 1000000007 EPS = 0.000000001 EPS 0.000000001 class Point():
    def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
  Point def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
  __init__ self.x = arg_x self.x self x arg_x self.y = arg_y self.y self y arg_y self self arg_x arg_x arg_y arg_y def calc_len(a,b):
    from math import sqrt
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))
  calc_len from math import sqrt return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)) sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)) sqrt (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) (a.x-b.x)*(a.x-b.x) a.x-b.x a.x a x b.x b x a.x-b.x a.x a x b.x b x (a.y-b.y)*(a.y-b.y) a.y-b.y a.y a y b.y b y a.y-b.y a.y a y b.y b y a a b b x1,y1,x2,y2 = map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 p1 = Point(x1,y1) p1 Point(x1,y1) Point x1 y1 p2 = Point(x2,y2) p2 Point(x2,y2) Point x2 y2 print("%.10f"%calc_len(p1,p2)) print "%.10f"%calc_len(p1,p2) "%.10f" calc_len(p1,p2) calc_len p1 p2 x2,y2 = map(float,input().split()) map(float,input().split()) x2 y2 = map(float,input().split()) map(float,input().split()) y2 p2 = Point(x2,y2) Point(x2,y2) p2 y1,x2,y2 = map(float,input().split()) map(float,input().split()) y1 x1,y1,x2,y2 = map(float,input().split()) map(float,input().split()) x1 MOD = 1000000007 1000000007 MOD EPS = 0.000000001 0.000000001 EPS p1 = Point(x1,y1) Point(x1,y1) p1 class Point():
    def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
  class Point():
    def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
  Point def calc_len(a,b):
    from math import sqrt
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))
  def calc_len(a,b):
    from math import sqrt
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))
  calc_len BIG_NUM = 2000000000 2000000000 BIG_NUM
from enum import Enum
import sys
 
BIG_NUM = 2000000000
MOD = 1000000007
EPS = 0.000000001
 
class Point():
    def __init__(self,arg_x,arg_y):
        self.x = arg_x
        self.y = arg_y
 
def calc_len(a,b):
    from math import sqrt
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))
 
x1,y1,x2,y2 = map(float,input().split())
 
p1 = Point(x1,y1)
p2 = Point(x2,y2)
 
print("%.10f"%calc_len(p1,p2))
